The present invention relates generally to the field of neurological and physiological dysfunctions associated with Alzheimer""s Disease. More particularly, the invention is concerned with the identification, isolation and cloning of genes which when mutated are associated with Alzheimer""s Disease as well as their transcripts. gene products and associated sequence information and neighbouring genes. The present invention also relates to methods for diagnosing and detecting carriers of the genes, and to Alzheimer""s Disease diagnosis and gene therapy using recombinant technologies and therapy using the information derived from the DNA, protein, and the metabolic function of the protein.
In order to facilitate reference to various journal articles, a listing of the articles is provided at the end of this specification.
Alzheimer""s Disease (AD) is a degenerative disorder of the human central nervous system characterized by progressive memory impairment and cognitive and intellectual decline during mid to late adult life (Katzman, 1986). The disease is accompanied by a constellation of neuropathologic features principal amongst which are the presence of extracellular amyloid or senile plaques and the neurofibrillary degeneration of neurons. The etiology of this disease is complex, although in some families it appears to be inherited as an autosomal dominant trait. However, even amongst these inherited forms of AD, there are at least three different genes which confer inherited susceptibility to this disease (St. George-Hyslop et al., 1990). The xcex54 (Cys112Arg) allelic polymorphism of the Apolipoprotein E (ApoE) gene has been associated with AD in a significant proportion of cases with onset late in life (Saunders et al., 1993; Strittmatter et al., 1993). Similarly, a very small proportion of familial cases with onset before age 65 years have been associated with mutations in the xcex2-amyloid precursor protein (APP) gene (Chartier-Harlin et al., 1991; Goate et al., 1991; Murrell et al., 1991; Karlinsky et al., 1992; Mullan et al., 1992). A third locus (AD3) associated with a larger proportion of cases with early onset AD has recently been mapped to chromosome 14q24.3 (Schellenberg et al., 1992; St George-Hyslop et al., 1992; Van Broeckhoven et al., 1992).
Although chromosome 14q carries several genes which could be regarded as candidate genes for the site of mutations associated with AD3 (e.g. cFOS, alpha-1-antichymotrypsin, and cathepsin G), most of these candidate genes have been excluded on the basis of their physical location outside the AD3 region and/or the absence of mutations in their respective open reading frames (Schellenberg, G D et al., 1992; Van Broeckhoven, C et al., 1992; Rogaev et al., 1993; Wong et al., 1993).
There have been several developments and commercial directions in respect of treatment of Alzheimer""s Disease and diagnosis thereof. Published PCT application WO 94 23049 describes transfection of high molecular weight YAC DNA into specific mouse cells. This method is used to analyze large gene complexes, for example the transgenic mice may have increased amyloid precursor protein gene dosage, which mimics the trisomic condition that prevails in Downs Syndrome, and allows the generation of animal models with xcex2-amyloidosis similar to that prevalent in individuals with Alzheimer""s Disease. Published international application WO 94 00569 describes transgenic non-human animals harbouring large transgenes such as the transgene comprising a human amyloid precursor protein gene. Such animal models can provide useful models of human genetic diseases such as Alzheimer""s Disease.
Canadian Patent application No. 2096911 describes a nucleic acid coding for amyloid precursor protein-cleaving protease, which is associated with Alzheimer""s Disease and Down""s syndrome. The genetic information may be used to diagnose Alzheimer""s Disease. The genetic information was isolated from chromosome 19. Canadian patent application 2071105, describes detection and treatment of inherited or acquired Alzheimer""s Disease by the use of YAC nucleotide sequences. The YACs are identified by the numbers 23CB10, 28CA12 and 26FF3.
U.S. Pat. No. 5,297,562, describes detection of Alzheimer""s Disease associated with trisomy of chromosome 21. Treatment involves methods for reducing the proliferation of chromosome 21 trisomy. Canadian Patent application No. 2054302 describes monoclonal antibodies which recognize a human brain cell nucleus protein encoded by chromosome 21 and are used to detect changes or expression due to Alzheimer""s Disease or Down""s Syndrome. The monoclonal antibody is specific to a protein encoded by human chromosome 21 and is found in large pyramidal cells of human brain tissue.
By extensive effort and a unique approach to investigating the AD3 region of chromosome 14q, the Alzheimer""s related membrane protein (ARMP) gene (or presenilin I (PS1) gene has been isolated, cloned and sequenced from within the AD3 region on chromosome 14q24.3. In addition, direct sequencing of RT-PCR products spanning this 3.0 kb cDNA transcript isolated from affected members of at least eight large pedigrees linked to chromosome 14, has led to the discovery of missense mutations in each of these different pedigrees. These mutations are absent in normal chromosomes. It has now been established that the PS1 (or ARMP) gene is causative of familial Alzheimer""s Disease type AD3. In realizing this link, it is understood that mutations in this gene can be associated with other cognitive, intellectual, or psychological diseases such as cerebral hemorrhage, schizophrenia. depression, mental retardation and epilepsy. These clinical diagnoses and phenotypes are present in these AD families and these phenotypes have been seen in mutations of the APP protein gene. The Amyloid Precursor Protein (APP) gene is also associated with inherited Alzheimer""s Disease. The identification of both normal and mutant forms of the PS1 gene and gene products has allowed for the development of screening and diagnostic tests for PS1 utilizing nucleic acid probes and antibodies to the gene product. Through interaction with the defective gene product and the pathway in which this gene product is involved, gene therapy, therapeutic intervention, manipulation and delivery are now made possible.
A second gene associated with AD has now been identified on human chromosome 1. This gene, the ES-1 or presenilin II (PS2) gene, also has been isolated and cloned. Mutations of this gene have been identified in patients with early onset familial AD. The PS2 (or ES-1) gene and protein have been shown to have high degrees of sequence homology at both the nucleic acid and amino acid sequence levels, and share major structural similarities, including conserved regions, tissue-specific alternative splicing patterns and predicted tertiary structure. Thus, they are believed to be representatives of a new gene family, the presenilins.
Non-human homologues of the PS1 and PS2 genes and proteins have now been identified, isolated and cloned. Amongst those disclosed herein are the murine homologue (PS1 ) of human PS1, a C. elegans member (SEL-12), and a D. melanogaster member (DmPS) of the presenilin gene family. Each of these genes and proteins have been identified on the basis of their high degrees of homology to the PS1/PS2 genes.
Various aspects of the invention are summarized as follows. In accordance with a first aspect of the invention, a purified mammalian polynucleotide is provided which codes for Alzheimer""s related membrane protein (ARMP) or presenilin I (PS1). The polynucleotide has a sequence which is the functional equivalent of the DNA sequence of ATCC deposit 97124, deposited Apr. 28, 1995. The mammalian polynucleotide may be in the form of DNA, genomic DNA, cDNA, mRNA and various fragments and portions of the gene sequence encoding PS1. The mammalian DNA is conserved in many species, including humans and rodents, for example mice; the DNA is conserved also in all other non-mammalian vertebrates and most invertebrate organisms.
Purified human nucleotide sequences which encode mutant PS1 include those having mutations at nucleotide position (i) 685, Axe2x86x92C (A is replaced by C); (ii) 737, Axe2x86x92G; (iii) 986, Cxe2x86x92A, iv) 1105, Cxe2x86x92G; (v) 1478, Gxe2x86x92A; (vi) 1027, Cxe2x86x92T; (vii) 1102, Cxe2x86x92T; and (viii) 1422, Cxe2x86x92G of SEQ ID NO:1 as well as in the cDNA sequence of a further human clone of a sequence identified by SEQ ID NO:133.
The nucleotide sequences encoding both PS1 and PS2 have an alternative splice form in the gene""s open reading frame. The human cDNA sequence which codes for PS1 has SEQ ID NO:1 as well as SEQ ID NO:133 as sequenced in another human clone. The mouse sequence which encodes mPS1 has SEQ ID NO:3, as well as SEQ ID NO:135 derived from a further clone containing the entire coding region. Various DNA and RNA probes and primers may be made from appropriate polynucleotide lengths selected from the sequences. Portions of the sequence also encode antigenic determinants of these presenilins.
Suitable expression vectors comprising the nucleotide sequences are provided along with suitable host cells transfected with such expression vectors.
In accordance with another aspect of the invention, purified mammalian Alzheimer""s related membrane protein (ARMP) or presenilin I (PS1) is provided. The purified protein has an amino acid sequence encoded by polynucleotide sequence as identified above which for the human is SEQ ID NO:2 and SEQ ID NO:134 (derived from another clone). The mouse PS1 amino acid sequence is defined by and SEQ ID NO:4, which is translated from another clone containing the entire coding region. The purified protein may have substitution mutations selected from the group consisting of the following positions identified in SEQ ID NO:2 and SEQ ID NO:134: (i) M 146 L; (ii) H 163 R; (iii) A 246 E; (iv) L 286 V; (v) C 410 Y: (vi) A 260 V; (vii) A 285 V; and (viii) L 392 V.
In accordance with another aspect of the invention, polyclonal and monoclonal antibodies raised to specific predicted sequences of the presenilin proteins are provided. Polypeptides of at least six amino acid residues are provided. The polypeptides of six or greater amino acid residues may define antigenic epitopes of a presenilin. Monoclonal antibodies having suitably specific binding affinity for the antigenic regions of a presenilin are prepared by use of corresponding hybridoma cell lines. In addition, other polyclonal antibodies may be prepared by inoculation of animals with suitable peptides or holoprotein which add suitable specific binding affinities for antigenic regions of a presenilin.
In accordance with another aspect of the invention. an isolated DNA molecule is provided which codes for E5-1 protein.
In accordance with another aspect of the invention, purified PS2 protein is provided. having amino acid SEQ ID NO: 137.
In accordance with another aspect of the invention a bioassay is provided for determining if a subject has a normal or mutant PS1 or PS2, where the bioassay comprises providing a biological sample from the subject. conducting a biological assay on the sample to detect a normal or mutant gene sequence coding for PS1 or PS2, a normal or mutant PS1 or PS2 amino acid sequence, or a normal or defective protein function.
In accordance with another aspect of the invention, a process is provided for producing PS1 or PS2 comprising culturing one of the above described transfected host cells under suitable conditions, to produce the presenilin by expressing the DNA sequence. Alternatively, a PS1 or PS2 protein may be isolated from mammalian cells in which the presenilin is normally expressed.
In accordance with another aspect of the invention, is a therapeutic composition comprising PS1 or PS2 and a pharmaceutically acceptable carrier.
In accordance with another aspect of the invention, a recombinant vector for transforming a mammalian tissue cell to express therapeutically effective amounts of PS1 or PS2 in the cells is provided. The vector is normally delivered to the cells by a suitable vehicle. Suitable vehicles include vaccinia virus, adenovirus, adeno associated virus, retrovirus, liposome transport, neuraltropic viruses, Herpes simplex virus and other vector systems.
In accordance with another aspect of the invention, a method of treating a patient deficient in normal PS1 or PS2 comprising administering to the patient a therapeutically effective amount of the protein targeted at a variety of patient cells which normally express the presenilin. The extent of administration of normal PS1 or PS2 being sufficient to override any effect the presence of the mutant presenilin may have on the patient. As an alternative to protein, suitable ligands and therapeutic agents such as small molecules and other drug agents may be suitable for drug therapy designed to replace the protein and defective presenilin, displace mutant presenilin, or to suppress its formation.
In accordance with another aspect of the invention, an immunotherapy for treating a patient having Alzheimer""s Disease comprises treating the patient with antibodies specific to the mutant presenilin to reduce biological levels or activity of the mutant protein in the patient. To facilitate such amino acid therapy, a vaccine composition may be provided for evoking an immune response in a patient of Alzheimer""s Disease where the composition comprises a mutant PS1 and a pharmaceutically acceptable carrier with or without a suitable excipient. The antibodies developed specific to the mutant PS1 could be used to target appropriately encapsulated drugs/molecules, specific cellular/tissue sites. Therapies utilizing specific ligands which bind to normal or wild type PS1 and which augment normal function of PS1 in membranes and/or cells or inhibits the deleterious effect of the mutant protein are also made possible.
In accordance with another aspect of the invention, a transgenic animal model for Alzheimer""s Disease which has the mammalian polynucleotide sequence with at least one mutation which when expressed results in mutant PS1 or PS2 in the animal cells and thereby manifests a phenotype. For example, the human Prion gene when over-expressed in rodent peripheral nervous system and muscle cells causes a quite different response in the animal than the human. The animal may be a rodent and is preferably a mouse, but may also be other animals including rat, pig, D. melanogaster, C. elegans (nematode), all of which are used for transgenic models. Yeast cells can also be used in which a presenilin sequence is expressed from an artificial vector.
In accordance with another aspect of the invention a transgenic mouse model for Alzheimer""s Disease has the mouse gene encoding a human or murine PS1 or PS2 homologue mutated to manifest the symptoms. The transgenic mouse may exhibit symptoms of cognitive memory loss or behavioural disturbances. In addition or alternatively. the symptoms may appear as another cellular tissue disorder such as in mouse liver. kidney, spleen, bone marrow or other organs in which the presenilin gene product is normally expressed.
In accordance with another aspect of the invention, the presenilin proteins and nucleic acids may be used in the screening of small molecules which will be candidates for drug therapy of Alzheimer""s and related diseases. In one series of embodiments, small molecules may be screened for their ability to bind to a persenilin, especially human PS1 or PS2. In particular, assays are provided which may be used to identify small molecules which will bind selectively or preferentially to either the normal or mutant forms of PS1 or PS2. Such small molecules may be further tested using the animal models disclosed mergon to further evaluate their therapeutic utility. In another series of embodiments, compounds may be tested for their ability to induce or respress expression of the presenilins, especially human PS1 or PS2. Thus, assays are provided in which the ability of a compound to alter the levels of presenilin mRNA transcripts or protein in a cell or cell culture is tested. In preferred embodiments, the 5xe2x80x2 regulatory region of a presenilin gene, especially a human PS1 or PS2 gene, are operatively joined to a reporter gene and cells are transformed with this recombinant construct. Such recombinant cells may then be used in high through-put assays for compounds which affect the expression of the presenilins.
In accordance with another aspect of the invention, the proteins of the invention can be used as starting points for rational drug design to provide ligands, therapeutic drugs or other types of small chemical molecules. Alternatively, small molecules or other compounds identified by the above-described screening assays may serve as xe2x80x9clead compoundsxe2x80x9d in rational drug design.